This invention relates generally to brush seals and more particularly to a brush seal for a gas turbine engine.
A gas turbine engine operates according to well known principles wherein an incoming stream of atmospheric air flows through the engine along an axially extending flow path. At least a portion of the incoming air is compressed in a compressor section of the engine and then mixed with fuel and burned in a combustor section to produce a high energy, high temperature exhaust gas stream. The hot gas stream exits the combustor and subsequently passes through a turbine section that extracts energy from the exhaust gas stream to power the compressor and provide useful work such as powering an aircraft in flight.
Uncontrolled leakage of gases--such as atmospheric air, exhaust gases, or other--within the engine contributes to a reduced engine efficiency. Seals are used to control this energy loss by interposing them in a leakage path to reduce the volume or mass of gas passing from one part of the engine to another. Labyrinth seals have been commonly used in gas turbine engines for sealing between relatively movable components. However, the use of brush seals as a substitute for labyrinth seals is also known.
A conventional brush seal typically includes a plurality of similar or identical seal stages with each stage including a bristle pack having a plurality of bristles. The bristle pack of each stage is disposed between a front plate (i.e., a plate facing the higher pressure) and a back plate with adjacent stages being spaced apart a specified distance. The bristles usually are disposed at about a forty five degree angle to a radius drawn from the engine centerline. A brush seal is typically attached along its outer radial edge to a stationary engine part with the radially inner, free ends of the bristles disposed in a sealing engagement with a sealing surface on a rotating engine part. Brush seals are not intended to function so as to completely seal one engine section from another, but rather rely upon the tortuous flow path created between the bristles to reduce gas flow therethrough and to control the pressure drop between the engine sections. Typically, the leakage flow and pressure drop are in the same direction for each stage of the brush seal.
While the use of multiple stages improves the effectiveness of conventional brush seals, it can cause the brush seal to be come bulky and difficult to install in many engine locations. Furthermore, the large number of support plates required for multiple stages increases the cost and weight of the seal.
Accordingly, there is a need for a multi-stage brush seal for gas turbine engines that is relatively easy to install and uses fewer parts than conventional multi-stage brush seals.